3D tube with sharp corners and uniform radius?
This method will only work well for angles less than 90°:


Set your curve to 3D and bevel it with circle curve, just as you would normally.
Then add solidify modifier, check Even Thickness and High Quality Normals, set thickness to negative value:


Then select that circle, go to editmode, and scale it down as you can, to a point. Stop when the tube starts displacing - that will be floating point limitations
You should end up with an ok tube with sharp turns and even thickness, it wont be perfect but I can't think of another way.